It seems well established that experimental animals may be predisposed to chemical carcinogenesis by varying levels of dietary fat, fats of various origins, and degree of lipid saturation. Although, in many cases, the magnitude and direction of response is dependent upon specific initiating chemicals, dose, and the respective target tissue, some generalizations concerning dietary role in cancer are beginning to emerge. Unlike chemical carcinogenesis, the role of diet in photocarcinogenesis has been virtually ignored although dietary involvement in UV-induced skin cancer was suggested over 40 years ago. However, it was recently demonstrated that state of dietary lipid saturation significantly affected the beneficial modification of photocarcinogenesis by antioxidants. These studies suggested that salutary responses to UV might be achieved through dietary modification. In addition to this goal, it is imperative to determine optimum dietary parameters through which beneficial responses to dietary antioxidants can be maximized. Specific objectives are to determine [1] levels of unsaturated dietary lipid that enhance photocarcinogenesis [2] levels of dietary fat that act antagonistically to antioxidant modificaion [3] whether dietary fat acts as a promoter of photocarcinogenesis [4] whether UV and diet predispose to other environmental carcinogens.